Distribution of subsurface temperature in the Kanto Plain, Japan; estimation of regional groundwater flow system and surface warming

摘要

Temperature-depth profiles and hydraulic heads were measured on 88 observation wells in the Kanto Plain. Subsurface temperature distribution in the Kanto Plain is assumed that it is strongly affected by heat advection due to groundwater flow. The high temperature area is located in lowlands around the Kinu River, the Tone River and the central part of the plain. On the other hand, the low temperature area is distributed in highlands such as hills and uplands located in the surrounding of the plain. Considering the observed distribution of subsurface temperatures and hydraulic heads, we estimated that there are two local groundwater flow systems which discharge to the Tone River and the Kinu River, and not regional groundwater flow system, in which the water is recharged in the surroundings of the plain and is discharges to the central part of the plain. Moreover, it was observed that 30 temperature-depth profiles have minimum temperature. The distribution of the depth of minimum temperature in the temperature-depth profile has tendency that the depth in the recharge area is deeper than that in the discharge area. This tendency indicates the existence of the regional groundwater flow system in the Kanto Plain.